char schar

(char string index) -- (schar string index)

Returns the character at the 0-based index of string. char and schar behave identically here; in Common Lisp schar is the simple-string variant, but rontolisp treats them the same. The WASM backend indexes strings by byte, so indexing is well-defined for ASCII text only.

Both are also setf places: (setf (schar s i) c) / (setf (char s i) c) replaces the character at i and returns c. The interpreter mutates the string in place; the compiled backends rebuild the string and rebind it, so the string expression must be a variable there, and an alias made before the write still sees the old content.